INTERFEROMETRIC METHOD AND APPARATUS FOR LINEAR DETECTION OF MOTION FROM A SURFACE
An apparatus and a method for detecting surface motion of an object subject to ultrasound are disclosed. The method comprises generating a laser beam, dividing the laser beam into a reference beam and an object beam to be directed onto the surface, thereby producing a scattered object beam, introducing a frequency shift between the reference beam and the scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, detecting the interference between the scattered object beam and the frequency shifted reference beam using a plurality of detecting elements to generate a plurality of electrical interference signals, wherein the electrical interference signals each comprise a wanted signal component indicative of the surface motion and a noise signal component, and processing the electrical interference signals to determine the surface motion of the object.
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1. Field of the Invention
The present invention relates generally to interferometric systems and methods for detection of small transient surface motion and particularly for detection of very small transient surface motion of an object subjected to ultrasound.
2. Background Art
Interferometry is a well known technique for measuring the phase difference between two or more optical beams. Two-beam interferometers, where one of the optical beams is back reflected by an object surface and the other beam is used as a reference, are used to monitor small deformations on an object or workpiece under test or small displacements of a surface of an object or workpiece under test. Laser ultrasonics can advantageously be used for nondestructive testing in order to measure the thickness of objects or to monitor defects in materials. When industrial applications involve the inspection of an optically rough surface, the ultrasonic information is encoded in a laser beam with speckles.
For detection on optically rough surfaces, the optical sensor must be able to efficiently process the back reflected speckled light. Three different types of interferometers have been previously proposed and developed to efficiently process speckled light for detection of small transient ultrasonic signals: confocal Fabry-Perot interferometers (CFP), adaptive interferometers based on two-wave mixing in photorefractive crystals (TWM), and Multi-channel random-quadrature (MCRQ) interferometers.
With the CFP and TWM interferometers, processing the speckles is carried out optically, and a single photodetector is then used to detect the demodulated signal. With the recently developed MRCQ interferometer, as described in U.S. patent application Ser. No. 10/583,954, processing the multiple speckles is carried out electronically using an array of photodetectors instead of a single photodetector. Each detector element of the array is optimized for single-speckle detection. As shown in
The phases of the portions of the interference beam arriving at the detector elements are random and not correlated with each other due to the speckled interference beam that results from a rough surface of the object whose displacement is measured. Thus, every detector of the detector array 38, 39 receives another speckle pattern with random and non-correlated phases. A processing circuit used with the MRCQ interferometer is also described in U.S. patent application Ser. No. 10/583,954 and shown in
As an example,
Furthermore, also for signals with ultrasonic frequencies of more than a few tens of MHz, demodulation based on signal rectification is no longer efficient. With increasing detection bandwidths, the noise amplitude also increases and the signal is often of smaller amplitude.
Thus, the rectification-demodulation is strongly influenced by the noise amplitude. The noise superimposes a DC offset to the signal, which degrades the rectification process.
Linear-demodulation for detection of signals at high ultrasonic frequency or of very small amplitude is proposed to overcome the above mentioned limitations.
SUMMARY OF INVENTIONIn a first aspect, the present disclosure relates to a method for detecting surface motion of an object subject to ultrasound. The method comprises generating a laser beam, dividing the laser beam into a reference beam and an object beam to be directed onto the surface, thereby producing a scattered object beam, introducing a frequency shift between the reference beam and the scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, detecting the interference between the scattered object beam and the frequency shifted reference beam using a plurality of detecting elements to generate a plurality of electrical interference signals, wherein the electrical interference signals each comprise a wanted signal component indicative of the surface motion and a noise signal component, and processing the electrical interference signals to determine the surface motion of the object.
In a second aspect, the present disclosure relates to a method for detecting surface motion of an object subject to ultrasound. The method comprises generating a laser beam, dividing the laser beam into a reference beam and an object beam to be directed onto the surface, wherein the normal on the surface of the object has an angle with the object beam, thereby producing a frequency shifted scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, wherein the object is in transverse motion with respect to the object beam, detecting the interference between the scattered object beam and the frequency shifted reference beam using a plurality of detecting elements to generate a plurality of electrical interference signals, wherein the electrical interference signals each comprise a wanted signal component indicative of the surface motion and a noise signal component, and processing the electrical interference signals to determine the surface motion of the object.
In a third aspect, the present disclosure relates to a laser interferometric apparatus for detecting surface motion of an object subject to ultrasound. The apparatus comprises a laser source for producing a laser beam, a beam splitter for dividing the laser beam into a reference beam and an object beam to be directed onto the surface, thereby producing a scattered object beam, a frequency shifting element for introducing a frequency shift between the reference beam and the scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, a detector with a plurality of detector elements for detecting the interference between the scattered object beam and the reference beam, resulting in a plurality of electrical interference signals each comprising a wanted signal component indicative of the surface motion and a noise signal component, and a processing unit for determining the surface motion of the object from the plurality of electrical interference signals.
In a fourth aspect, the present disclosure relates to a laser interferometric apparatus for detecting surface motion of an object subject to ultrasound. The apparatus comprises a laser source for producing a laser beam, a beam splitter for dividing the laser beam into a reference beam and an object beam to be directed onto the object/surface, wherein the normal on the surface of the object has an angle with the object beam, thereby producing a frequency shifted scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, wherein the object is in transverse motion with respect to the object beam, a detector for detecting the interference between the scattered object beam and the reference beam, resulting in a plurality of electrical interference signals each comprising a wanted signal component indicative of the surface motion and a noise signal component, the electrical interference signals each defining a channel, and a processing unit for determining the surface motion of the object from the plurality of electrical interference signals.
Other aspects, characteristics, and advantages of the invention will be apparent from the following detailed description.
Specific embodiments of the present disclosure will now be described in detail with reference to the accompanying Figures. Like elements in the various Figures are denoted by like reference numerals for consistency.
In general, embodiments of the present disclosure relate to apparatus and methods for detecting very small surface motion of an object subject to ultrasound. More specifically, embodiments of the present disclosure provide methods and apparatus for obtaining output signals from a multi-speckle random-quadrature (MRCQ) interferometer that are proportional to the small transient surface motion.
We will describe methods and apparatus for detection of very small signals in interferometers enabling linear signal demodulation. This is achieved by using a small frequency shift or a Doppler shift in one of the interferometer arms and by synchronizing the detection to this applied frequency/Doppler shift.
According to this embodiment, a low frequency shift fD 71 is introduced into the reference beam 18 by a frequency shifting cell 70. Examples of frequency shifting cells include, but are not limited to, acousto-optic modulators. For example, a combination of two acousto-optic modulators operating at different frequencies may be used in order to obtain the required low frequency shift from the difference of the modulator frequencies. Preferably, the frequency shift fD 71 is below the frequencies of the small ultrasonic displacement to be measured and above perturbations due to ambient noise. Ambient noise frequencies are typically smaller than around 10 kHz. For example, the ultrasonic frequency may be around 100 kHz. Generally, the frequency shift fD will be between around 1 kHz and 1 MHz and may preferably be selected to be smaller than around 100 kHz and greater than around 10 kHz.
According to another variant of the first preferred embodiment, the first beam splitter 20 is a polarizing beam splitter, dividing the laser beam 14 into two orthogonally linearly polarized object and reference beams 16, 18. A quarter-wave plate 37, as shown in
As the person skilled in the art will appreciate, other systems than the piezo cylinder 80 attached to the fiber end 46 to induce motion of the fiber end 46 may be implemented with the interferometric apparatus 200 according to embodiments disclosed herein. For example, a voice coil system may be used to induce back and forth motion of the fiber end 46 with respect to the object 24.
A Cassegrain optical system (not shown) comprising a reflector and a large aperture lens may also be used to couple the laser beam 14 into the multi-mode fiber 45. The reflector may be, for example, a small mirror or a prism.
Still referring to
The Faraday rotator 56 and the polarizing beam splitter 55 form an optical isolator, which offers protection for the laser and thus avoids any possible laser instability caused by laser light being back-reflected into the laser. The Faraday rotator 56 also maximizes the sensitivity of the apparatus by allowing to separate and independently detect the horizontal and the vertical polarization components of the optical interference signal 49, which exhibits scrambled polarization.
wherein λ is the wavelength of the laser light.
The sign ± in the above equation accounts for slightly different detection angles for the detector elements of on detector array. In addition, if, for example, the surface of the object is not flat, the surface normal changes its direction depending on the location of the object when it moves by the interferometric apparatus. Thus, the incidence angle αI varies, which leads to variations in the Doppler shift. If the corresponding frequency shift fD(αI) is still in the preferred frequency range as described above, the operation principle of the interferometric apparatus 300 according to embodiments disclosed herein is not affected.
As will be understood by the skilled person, in the interferometric apparatus of
Referring now to
The electrical interference signal from a detector element n of a detector array may be written as
VD(n)∝Iref+2√{square root over (Iobj(n)Iref)}·cos [φLF(t,n)+2πfDt+φUT(t)] (1)
where fD is the applied Doppler frequency shift, φUT(t) is the small-amplitude and high-frequency phase variation induced by ultrasound, and φLF(t) is the low frequency component of the phase (including the random speckle phase distribution and dependent on ambient noise), which fluctuates between 0 and 2π. Iobj(n) and Iref correspond to the intensities of the scattered object beam and the reference beam, respectively. It is assumed that the reference intensity is uniform on the detector array and much stronger than the scattered object intensity. As an example,
A sign ambiguity is due to the transfer function of the interferometric apparatus, i.e., the electrical interference signal VD(n). As shown in
The sign ambiguity is removed by looking at both the signal and its time derivative. This is done by separating the electrical interference signal into a high-frequency and a low frequency electrical signal, as described above. The high-frequency electrical signal VHF reads
VHF(n)∝−2√{square root over (Iobj(n)Iref)}·sin [φLF(t,n)+2πfDt]·φUT(t), (2)
and the low-frequency electrical signal VLF reads
VLF(n)∝Iref+√{square root over (Iobj(n)Iref)} cos [φLF(t,n)+2πfDt]. (3)
The time derivative of the low-frequency signal VLF is then carried out using the derivator circuit. The time derivative can be expressed as
After multiplication of the high-frequency electrical signal, Eq. (2), and the time derivative low-frequency electrical signal, Eq. (4), the resulting multiplied signal VMulti is
VMulti(n)∝A(n)·φUT(t), (5)
with
It appears from Eq. (6) that the sign of the transfer function is given by the coefficient A(n) and only depends on the sign of the term
Thus, due to the application of the Doppler frequency shift, the sign of the coefficient A(n) does not fluctuate due to ambient perturbations, and there is no sign ambiguity of the transfer function.
If the Doppler frequency shift is larger than the noise-induced phase perturbation:
the sign of the coefficient A(n) does not change and is given by the sign of fD, which depends on the direction of the induced motion.
After summation of all the multiplied signals from all the detector elements n of the detector arrays, the average output signal Vout(t) at the output of the summing amplifier is
The output signal is proportional to the small ultrasonic phase of interest and is thus indicative of the displacement of the object's surface. No stabilized quadrature detection scheme is required.
The linear system relies on the random nature of the speckled light. If a sufficient number of independent speckled multiplied signals are summed, it can be assumed that the resulting output signal corresponds to 50% of in-quadrature signals and 50% of out-of-quadrature signals. Summation over a large number of multiplied signals leads to
Thus, summation over a large number of elements n leads to a stable output signal where
From Eq. (9), it appears that the constant term, i.e., the output signal, is proportional to the Doppler shift, fD. In-quadrature signals (positive or negative) is detected if the condition
is fulfilled, leading to a full strength signal at the output of the detector. Out-of-quadrature signals are detected if [2πfDt+φLF(t,n)]=kπ, where k is a natural number. Then the signal at the output of the multiplier is VMulti(n)=0, and thus, it does not contribute to the output signal of interest. Only the in-quadrature signals are used for generating the stable output signal.
In the embodiments of the processing circuit shown in
Furthermore, in the embodiments as shown in
Advantageously, apparatus and methods of the present disclosure may provide at least one of the following advantages.
The linear detection scheme according to embodiments disclosed herein exhibits near ideal sensitivity. Very small signals may be detected, whereby the signals are proportional to the surface motion of the object. The linear detection scheme also provides for the knowledge of the direction of the surface displacement, and it is adapted to be used with a large range of ultrasonic frequencies.
Specifically, using frequency shifting with acousto-optic modulators (first embodiment shown in
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims
1. A method for detecting surface motion of an object subject to ultrasound, the method comprising:
- generating a laser beam;
- dividing the laser beam into a reference beam and an object beam to be directed onto the surface, thereby producing a scattered object beam;
- introducing a frequency shift between the reference beam and the scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency;
- detecting the interference between the scattered object beam and the frequency shifted reference beam using a plurality of detecting elements to generate a plurality of electrical interference signals, wherein the electrical interference signals each comprise a wanted signal component indicative of the surface motion and a noise signal component; and
- processing the electrical interference signals to determine the surface motion of the object.
2. The method according to claim 1, wherein the frequency shift is comprised between 1 kHz and 1 MHz and preferably between 10 kHz and 100 kHz.
3. The method according to claim 2, wherein the processing comprises:
- separating each of the electrical interference signals into a high-frequency electrical signal and a low-frequency electrical signal, whereby the high-frequency electrical signal comprises the wanted signal component;
- obtaining the time derivative of the low-frequency electrical signal; and
- deriving the wanted signal component from the high-frequency electrical signal and the time derivative of the low-frequency electrical signal.
4. The method according to claim 3, wherein the deriving comprises:
- multiplying the high-frequency signal with the time derivative of the low-frequency signal to obtain a resulting multiplied signal for each electrical interference signal; and
- summing the resulting multiplied signals to obtain an average output signal comprising substantially the wanted signal component.
5. The method according to claim 3, wherein the deriving comprises:
- separating each of the high-frequency electrical signals in a direct electrical signal and an inverted electrical signal;
- converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- selecting between the direct electrical signal and the inverted electrical signal using the binary logic signal to obtain a multiplexed electrical signal for each electrical interference signal; and
- summing the multiplexed electrical signals to obtain an average output signal comprising substantially the wanted signal component.
6. The method according to claim 3, wherein the deriving comprises:
- converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- rooting the high-frequency electrical signals toward either a non-inverting path or an inverting path using the binary logic signal;
- summing the high-frequency electrical signals rooted to the non-inverting path and summing the high-frequency electrical signals rooted to the inverting path to obtain a first output signal and a second output signal, respectively; and
- subtracting the first and the second output signal to obtain an average output signal comprising substantially the wanted signal component.
7. The method according to claim 3, wherein obtaining the time derivative of the low-frequency electrical signal comprises high-pass filtering of the low-frequency electrical signal.
8. The method according to claim 3, wherein separating the electrical interference signal comprises high-pass filtering and low-pass filtering of the electrical interference signal.
9. A method for detecting surface motion of an object subject to ultrasound, the method comprising:
- generating a laser beam;
- dividing the laser beam into a reference beam and an object beam to be directed onto the surface, wherein the normal on the surface of the object has an angle with the object beam, thereby producing a frequency shifted scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, wherein the object is in transverse motion with respect to the object beam;
- detecting the interference between the scattered object beam and the frequency shifted reference beam using a plurality of detecting elements to generate a plurality of electrical interference signals, wherein the electrical interference signals each comprise a wanted signal component indicative of the surface motion and a noise signal component; and
- processing the electrical interference signals to determine the surface motion of the object.
10. The method according to claim 9, wherein the frequency shift is comprised between 1 kHz and 1 MHz and preferably between 10 kHz and 100 kHz.
11. The method according to claim 10, wherein the processing comprises:
- separating each of the electrical interference signals into a high-frequency electrical signal and a low-frequency electrical signal, whereby the high-frequency electrical signal comprises the wanted signal component;
- obtaining the time derivative of the low-frequency electrical signal; and
- deriving the wanted signal component from the high-frequency electrical signal and the time derivative of the low-frequency electrical signal.
12. The method according to claim 10, wherein the deriving comprises:
- multiplying the high-frequency signal with the time derivative of the low-frequency signal to obtain a resulting multiplied signal for each electrical interference signal; and
- summing the resulting multiplied signals to obtain an average output signal comprising substantially the wanted signal component.
13. The method according to claim 10, wherein the deriving comprises:
- separating each of the high-frequency electrical signals in a direct electrical signal and an inverted electrical signal;
- converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- selecting between the direct electrical signal and the inverted electrical signal using the binary logic signal to obtain a multiplexed electrical signal for each electrical interference signal; and
- summing the multiplexed electrical signals to obtain an average output signal comprising substantially the wanted signal component.
14. The method according to claim 10, wherein the deriving comprises:
- converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- rooting the high-frequency electrical signals toward either a non-inverting path or an inverting path using the binary logic signal;
- summing the high-frequency electrical signals rooted to the non-inverting path and summing the high-frequency electrical signals rooted to the inverting path to obtain a first output signal and a second output signal, respectively; and
- subtracting the first and the second output signal to obtain an average output signal comprising substantially the wanted signal component.
15. The method according to claim 10, wherein obtaining the time derivative of the low-frequency electrical signal comprises high-pass filtering of the low-frequency electrical signal.
16. The method according to claim 10, wherein separating the electrical interference signal comprises high-pass filtering and low-pass filtering of the electrical interference signal.
17. A laser interferometric apparatus for detecting surface motion of an object subject to ultrasound, the apparatus comprising:
- a laser source for producing a laser beam;
- a beam splitter for dividing the laser beam into a reference beam and an object beam to be directed onto the surface, thereby producing a scattered object beam;
- a frequency shifting element for introducing a frequency shift between the reference beam and the scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency;
- a detector with a plurality of detector elements for detecting the interference between the scattered object beam and the reference beam, resulting in a plurality of electrical interference signals each comprising a wanted signal component indicative of the surface motion and a noise signal component; and
- a processing unit for determining the surface motion of the object from the plurality of electrical interference signals.
18. The apparatus according to claim 17, further comprising a beam combiner for generating the interference between the scattered object beam and the reference beam on the detector.
19. The apparatus according to claim 18, further comprising a second detector with a plurality of detector elements, wherein the beam combiner generates the interference between the scattered object beam and the reference beam on each of the detectors.
20. The apparatus according to claim 17, further comprising a multimode optical fiber into which the laser beam is coupled, wherein the beam splitter comprises an end facet of the multimode optical fiber and the interference between the scattered object beam and the reference beam is generated within the fiber.
21. The apparatus according to claim 17, wherein the processing unit comprises:
- one or a plurality of filters for separating the electrical interference signals of each channel into a high-frequency electrical signal and a low-frequency electrical signal, whereby the high-frequency electrical signal comprises the wanted signal component; and
- a derivator for obtaining the time derivative of the low-frequency electrical signal.
22. The apparatus according to claim 21, wherein the processing unit further comprises:
- a multiplier for multiplying the high-frequency signal with the time derivative of the low-frequency signal to obtain a resulting multiplied signal for each channel; and
- a summing amplifier for summing resulting multiplied signals of the channels to obtain an average output signal comprising substantially the wanted signal component.
23. The apparatus according to claim 21, wherein the processing unit further comprises:
- one or a plurality of amplifiers for separating the high-frequency electrical signals of each channel in a direct electrical signal and an inverted electrical signal;
- a comparator for converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- a switch for selecting between the direct electrical signal and the inverted electrical signal using the binary logic signal to obtain a multiplexed electrical signal; and
- a summing amplifier for summing the multiplexed electrical signals of the channels to obtain an average output signal comprising substantially the wanted signal component.
24. The apparatus according to claim 21, wherein the processing unit further comprises:
- a comparator for converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- a switch for rooting the high-frequency electrical signals toward either a non-inverting path or an inverting path using the binary logic signal;
- a summing amplifier for summing the high-frequency electrical signals rooted to the non-inverting path and a summing amplifier for summing the high-frequency electrical signals rooted to the inverting path to obtain a first output signal and a second output signal, respectively; and
- a differential amplifier for subtracting the first and the second output signal to obtain an average output signal comprising substantially the wanted signal component.
25. The apparatus according to claim 21, wherein the derivator comprises a first-order high-pass filter.
26. The apparatus according to claim 17, wherein the frequency shifting element comprises at least one selected from the group consisting of at least two acousto-optic modulators disposed in the reference beam and a Piezo mirror disposed in the reference beam.
27. The apparatus according to claim 20, wherein the frequency shifting element comprises at least one selected from the group consisting of a piezo cylinder attached to an end of the multimode optical fiber and a voice coil system attached to an end of the multimode optical fiber.
28. A laser interferometric apparatus for detecting surface motion of an object subject to ultrasound, the apparatus comprising:
- a laser source for producing a laser beam;
- a beam splitter for dividing the laser beam into a reference beam and an object beam to be directed onto the object/surface, wherein the normal on the surface of the object has an angle with the object beam, thereby producing a frequency shifted scattered object beam, wherein the frequency shift is smaller than the ultrasonic frequency, wherein the object is in transverse motion with respect to the object beam;
- a detector for detecting the interference between the scattered object beam and the reference beam, resulting in a plurality of electrical interference signals each comprising a wanted signal component indicative of the surface motion and a noise signal component, the electrical interference signals each defining a channel; and
- a processing unit for determining the surface motion of the object from the plurality of electrical interference signals.
29. The apparatus according to claim 28, further comprising a beam combiner for generating the interference between the scattered object beam and the reference beam on the detector.
30. The apparatus according to claim 29, further comprising a second detector with a plurality of detector elements, wherein the beam combiner generates the interference between the scattered object beam and the reference beam on each of the detectors.
31. The apparatus according to claim 28, further comprising a multimode optical fiber into which the laser beam is coupled, wherein the beam splitter comprises an end facet of the multimode optical fiber and the interference between the scattered object beam and the reference beam is generated within the fiber.
32. The apparatus according to claim 28, wherein the processing unit comprises:
- one or a plurality of filters for separating the electrical interference signals of each channel into a high-frequency electrical signal and a low-frequency electrical signal, whereby the high-frequency electrical signal comprises the wanted signal component; and
- a derivator for obtaining the time derivative of the low-frequency electrical signal.
33. The apparatus according to claim 32, wherein the processing unit further comprises:
- a multiplier for multiplying the high-frequency signal with the time derivative of the low-frequency signal to obtain a resulting multiplied signal for each channel; and
- a summing amplifier for summing resulting multiplied signals of the channels to obtain an average output signal comprising substantially the wanted signal component.
34. The apparatus according to claim 32, wherein the processing unit further comprises:
- one or a plurality of amplifiers for separating the high-frequency electrical signals of each channel in a direct electrical signal and an inverted electrical signal;
- a comparator for converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- a switch for selecting between the direct electrical signal and the inverted electrical signal using the binary logic signal to obtain a multiplexed electrical signal; and
- a summing amplifier for summing the multiplexed electrical signals of the channels to obtain an average output signal comprising substantially the wanted signal component.
35. The apparatus according to claim 32, wherein the processing unit further comprises:
- a comparator for converting the time derivative of the low-frequency electrical signal to a binary logic signal;
- a switch for rooting the high-frequency electrical signals toward either a non-inverting path or an inverting path using the binary logic signal;
- a summing amplifier for summing the high-frequency electrical signals rooted to the non-inverting path and a summing amplifier for summing the high-frequency electrical signals rooted to the inverting path to obtain a first output signal and a second output signal, respectively; and
- a differential amplifier for subtracting the first and the second output signal to obtain an average output signal comprising substantially the wanted signal component.
36. The apparatus according to claim 32, wherein the derivator comprises a first-order high-pass filter.
Type: Application
Filed: Nov 7, 2008
Publication Date: May 14, 2009
Patent Grant number: 7864338
Applicant: BOSSA NOVA TECHNOLOGIES, LLC (Venice, CA)
Inventor: Bruno Pouet (Los Angeles, CA)
Application Number: 12/267,336
International Classification: G01B 11/02 (20060101);